Three-unit electrical connector

ABSTRACT

The electrical connector includes two plugs which mate with an intermediate receptacle. A yieldable coupling connects the receptacle and one of the plugs, permitting separation upon the exertion of a predetermined force. The other plug includes spring-pressed pins which enter transverse slots in the receptacle upon limited relative separating movement, holding the parts in a dead-face position with the receptacle in front of the other plug and the electrical circuit interrupted. Therefore, an outward pull on the first plug initially moves the other plug to the dead-face position, following which the first plug is separated from the receptacle. The receptacle is removable from the other plug by first rotating it, which moves the springpressed pins out of the transverse slots and permits complete separation of the parts.

United States Patent [721 lnventors D vi T- A 2,735,906 2/1956 Avrunin 1 ZOO/51.09 Norma C- Robmanv both 1 nni g, 2,986,613 5/1961 Figueira ZOO/51 O9 Calif. 3,038,972 6/1962 Lagier ZOO/51.09 (21] Appl No. 815,053 3,078,435 2/1963 Berry 339/111 [22] Filed Apr. 10,1969 3,083,274 3/1963 Sparkes.. 339/91 X 1 Palehled A g-10.1971 3,196,228 7/1965 Colenutt. 339/1 1 l X [731 Assignee The Deutsch Company Electronic 3,360,764 12/1967 Bac 339/1 1 1 X gzr z z g Primary Examinerlan A. Calvert Allorney-Gausewitz & Rothenberg [54] g g imz fitig g CONNECTOR ABSTRACT: The electrical connector includes two plugs g which mate with an intermediate receptacle. A yieldable [52] U.S.Cl 339/42, coupling connegts the receptacle and one of [he lug per: Z /51.09, 339/91, 339/1 11 mitting separation upon the exertion of a predetermined [51 Int. Cl .1101! 13/44, force, The other plug includes spring-pressed pins which enter H 11 /54, HOlr 13/60 transverse slots in the receptacle upon limited relative separatl l Field 01 Search n /41 ing movement, holding the parts in a dead-face position with 75, 91 M, 1 1 l; ZOO/51.09, 51.07 the receptacle in front of the other plug and the electrical circuit interrupted. Therefore, an outward pull on the first plug 156] Rekrences C'Ied initially moves the other plug to the dead-face position, fol- UNITED STATES PATENTS lowing which the first plug is separated from the receptacle. 1 0 3 759 1 1912 Fisher 339 1 11 UX The receptacle is removable from the other plug by first rotat- 1 995,195 3/1935 Tornblom 339/111 ux g it, Whieh moves the sprihepressed P out of the trans- 2,724,093 1 1/1955 Preston 339/1 1 1 x verse S1015 ahd Permits complete Separation of the P i i 25 a4 75 73 13 I i 41 1 in" IJG I 82 l J6 9 n 3 59 JG 7 :7- 7a ,3 :5 4:

7a 1/ a J/ 60 THREE-UNIT ELECTRICAL CONNECTOR BACKGROUND OF THE INVENTION 1. Field of the Invention I This invention relates to an electrical connector.

2. The Prior Art The electrical circuits of airborne missile-firing systems encounter various severe problems affecting both safety and maintenance. Such a system may include an electrical connector in the circuit that supplies the current to ignite the rocket to propel the missile, arranged so that the connector is pulled apart when the missile leaves the launcher. As this takes place, it is hazardous for arcing to occur between the two portions of the connector that are separated. Also, the heat of the rocket blast will destroy the stationary portion of the connector at the launcher. Replacement is necessary before the system can be reused. If some means is provided to shield the stationary connector section from the rocket exhaust, the protective device will become destroyed as it is subjected to the heat of the rocket gases, even if the stationary connector section is undamaged. The protective device then becomes an element for removal and replacement after each firing. It may be difficult or impossible, in view of extreme weather conditions, to manipulate tooling to accomplish such an operation. As a result, the missile-firing system is rendered unusable. Another difficulty resides in the danger of inadvertent firing of the missile after it has moved slightly from its initial position, but has not left the launcher. Subsequent shifting of the position of the missile may cause the circuit to become reestablished as the connector is moved back to the mated position, and result in an undesired firing of the missile. Electrical connectors in the past have left these problems unsolved.

SUMMARY OF THE INVENTION The present invention overcomes the above-noted difficulties, providing an improved electrical connector suitable for a missile-firing system. It includes one plug that is attached to the missile, a second plug that is permanently attached to the rocket-launching unit and a receptacle intermediate the plugs. Electrical contacts are carried by the plugs and the receptacle, which are engaged when the parts are in their mated position, thereby completing the circuit between the plugs.

A yieldable coupling device is provided between the receptacle and the plug on the missile. This may include a plurality of balls received in a groove in the receptacle, held thereby a spring which may be overcome upon the exertion of a predetermined outward force by the missile. However, a lesser force will cause the receptacle to begin separating from the stationary plug. A pair of spring-pressed pins extends through openings in a tubular portion of the stationary plug to bear against the surface of the receptacle when the parts are mated. Aligned with the pins are recesses in the form of transverse slots into which the ends of the pins move when the receptacle is pulled away from the stationary plug a limited amount. The parts are proportioned such that the contacts are disengaged when this position is reached, so that the electrical circuit is broken. The pins hold the receptacle to the stationary plug in this dead-face position. Subsequently, the yieldable coupling between the receptacle and the plug on the missile will separate as the missile leaves the launcher, but no arcing can take place because of the prior interruption of the current path. The receptacle, held by the pins, remains in front of the stationary plug, protecting it from damage by the heat of the rocket.

The transverse slots also provide walls that prevent subsequent axial movement of the receptacle back into the stationary plug, so that the missile is disarmed in any event once a small amount of movement has taken place. However, the receptacle may be readily separated from the stationary plug by rotation, which removes the ends of the pins from the transverse slots. This is accomplishedwithout the use of tools.

The receptacle is provided with inclined edge ramps which engage the pins and cam them outwardly when the receptacle and stationary plug are to be mated. An outwardly projecting key acts as a stop which limits the axial movement but, upon predetermined rotation, is aligned with a keyway permitting further axial movement to bring the parts to the fully mated position. Upon this rotation, the 'pins are aligned with, but spaced from, the transverse slots. Removal and replacement of the receptacle, therefore, are hand operations, with no tools being needed.

An object of this invention is to provide an improved electrical connector having a dead-face arrangement for protecting a section of the connector.

Another object of this invention is to provide an improved electrical connector in which the electrical circuit is broken before the connector elements are separated.

A further object of this invention is to provide an electrical connector in which the electrical circuit is broken upon limited separating movement, and cannot be reestablished upon subsequent axial movement in .the opposite direction.

A still further object of this invention is to provide an electrical connector for a missile-firing system, having an intermediate portion which is a throwaway item protecting the stationary portion on the missile launcher, and removable by hand to avoid the necessity for the use of any tooling.

These and other objects will become apparent from the following detailed description taken in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of the connector of this inventron;

FIG. 2 is an exploded perspective view of the connector;

FIG. 3 is a longitudinal sectional view of the connector, taken along line 3-3 of FIG. 1, showing the connector in the fully mated position;

FIG. 4 is a view similar to FIG. 3, but illustrating the connector after it has been moved to thedead-face condition;

FIG. 5 is a view similar to FIG.--4,.-but illustrating the movable plug fully separated from the receptacle;

FIGS 6, 7, 8, 9 and 10 are transverse sectional views taken along lines 6-6, 7-7, 8-8, 9-9 and 10-10, respectively, of FIG. 3; 1

FIG. 11 is an enlarged fragmentary sectional view along line 1 1-11 of FIG. 9;

FIG. 12 is a perspective view, partially in phantom, illustrating the initial engagement of the pins of the stationary plug with the inclined end surfaces of the receptacle for movement to the mated position;

FIG. 13 is a perspective view similar to FIG. 1 1, showing the relationship of the pins of the stationary plug and the receptacle following axial advancement of the plug and receptacle, and relative rotation from the position .of FIG. 12; and

FIG. 14 is a perspective view similar to FIGS 11 and 12, illustrating the engagement of the stop pins in the transverse slots of the receptacle when the connector is in the dead-face position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The connector of this invention includes a plug 10, an additional plug 11 and a receptacle 12 that mates with both the plugs 10 and 11. Contacts are provided in the units 10, 11 and 12 to complete electrical circuits through the connector when it is in the mated position.

The receptacle 12 includes a tubular shell 13 having an exteriorly projecting annular flange 14 intermediate its ends. Within the shell 13 at its central portion is an insert 15 which rigidly carries elongated pins 16 that extend outwardly beyond either end of the insert 15. Typically, the insert 15 is made of glass, although certain plastics are suitable as well. Adjacent the radial faces of the insert 15 are sealing inserts l7 and 18 of a resilient elastomer, such as rubber.

The plug has a tubular shell 20, which at its forward end has an enlarged annular portion 21. Within the shell is an insert 22 of rigid plastic material, held in place by a nut 23 that engages the internally threaded rearward end portion of the plug shell 20. This holds a flange 24 of the insert 22 in engagement with a shoulder 25 in the interior of the plug shell 20. An exterior flange 26 on the nut 23 is provided with openings 27 for mounting the plug in a desired location. Typically, this will be in an airborne rocket-launching unit, where the flange 26 is attached to the structure carried by the aircraft.

Socket contacts 29 are carried by the rigid plastic insert 22 in the plug shell 20. Wires 30 extend inwardly through a resilient sealing insert 31 in the nut 23 with their ends stripped of insulation and joined to the socket contacts 29. When the connector is in its mated position shown in FIG. 3, the ends of the pins 16 are received in the socket contacts 29, thereby completing an electrical circuit from the receptacle to the wires 30. In the mated position of the plug 10 and receptacle 12, the end portion 32 of the receptacle shell 13 enters the annular space outwardly of the exterior of theforward end of the insert 22 in the enlarged forward cylindrical opening 33 in the plug shell 20.

The plug 11 includes a tubular shell 35 carrying a rigid plastic insert 36, generally similar to the insert 22. Socket contacts 37 are suitably mounted in the insert 36. Wires 38 extend inwardly through a resilient insert 39 to engage the socket contacts 37. The resilient insert 39 is received within a nut 40, which is threaded into the rearward end of the plug shell 35. A mounting flange 41, having openings 42, is provided at the end of the nut 40. This allows the plug 11 to be mounted in a desired location. When used in connection with a missile firing system, the flange 41 is attached to the rocket that is to be tired. In the mated position of the connector, the ends of the pins 16, to the right as the device is shown, enter the socket contacts 37, thereby forming an electrical connection. This completes circuits between the wires 30 and the wires 38. The right-hand end portion 43 of the receptacle shell 13 then is received in the annular space around the forward end of the insert 36 at the forward opening 44 in the plug shell 35.

A breakaway coupling mechanism interconnects the receptacle 12 and the plug 11 when they are in the mated position. This coupling arrangement includes a plurality of balls 45 that are received within frustoconical openings 46 which extend through the cylindrical wall of the forward end portion of the plug shell 35. The openings 46 are dimensioned so that the balls 45 may project a limited amount into the space between the insert 36 and the plug shell 35 at the opening 44. Two split annular sheet metal springs 47 and 48 circumscribe the forward end of the plug shell 35, positioned against axial movement by a forward flange 49 at the end of the plug shell, and a shoulder 50 inwardly of the flange 49. The inner spring member 47 is provided with slots 51 at the locations of the balls 45. The outer spring 48 biases the balls 45 inwardly toward the axis of the plug 11.

An annular groove 52 circumscribes the end portion 43 of the receptacle shell 13. This groove is arcuate in cross section, diverging outwardly from its central portion. When the parts are moved to the mated position, the end portion 43 of the receptacle 12 enters the opening 44 in the plug shell 35 and engages the inner surfaces of the balls 45. Continued relative axial movement causes the balls 45 to be pushed outwardly by the end portion 43 against the force of the spring 48. When the continued movement brings the groove 52 to the location of the balls 45, the latter members are moved inwardly by the spring 48 to enter the recess provided by the groove 52. This holds the plug 11 and receptacle 12 together in the mated position. However, the plug 11 and receptacle 12 may be separated by imposing an axial force of adequate magnitude tending to separate them. When the separating force is sufficiently high, the balls 45 are cammed outwardly through the reaction at the outwardly inclined side of the groove 52, overcoming the inward force of the spring 48. This moves the balls 45 out of the groove 52 so that the plug 11 and receptacle 12 are free to be pulled apart.

In order to assure proper electrical connection between the pins 16 and sockets 37 of the plug 11 and receptacle 12, respectively, an axially extending key 54 is provided on the receptacle 12, which enters an axially extending keyway 55 in the shell 35 of the plug 11. This allows the plug ll and receptacle 12 to be mated in only one relative rotational position.

A mechanism is included for the plug 10 and the receptacle 12 which allows the parts to move to a dead-face position, which is shown in FIGS. 4 and 5, in which the electrical circuit is broken, but the plug 10 and receptacle 12 are still held together and prevented from separation. This arrangement includes opposed radially positioned pins 57 and 58, which are located in openings 59 and 60 in the enlarged annular portion 21 of the plug shell 20. The pins 57 and 58 include flattened end portions 61 and 62 that extend throughthe inner portions of the openings 59 and 60 that are of reduced dimension longitudinally of the connector. The end portion 61 of the pin 57 is wider in the transverse direction of the connector than is the end portion 62 of the pin 58. The pins 57 and 58 are provided with flanges 63 and 64 engaged by the inner ends of compression springs 65 and 66. The outer ends of the springs 65 and 66 engage the inner ends of threaded members 67 and 68 that are received in the peripheral portion of the enlargement 21 of the plug shell 20. Therefore, the springs 65 and 66 bias the pins 57 and 58 radially inwardly toward positions where the end portions 61 and 62 project past the inner surface of the end of the plug shell 20 into the opening 33. The threaded members 67 and 68 are provided with central apertures that receive and help guide the outer ends ofthe pins 57 and 58.

Opposed inclined flat ramp surfaces 70 and 71 are located at the forward edge of the end portion 32 of the receptacle shell 13. The surfaces 70 and 71 taper radially outwardly and axially inwardly fromthe edge of the receptacle shell. The ramps 70 and 71 are for engagement by the end portions 61 and 62 of the pins 57 and 58 when the connector is to be mated. The surface 71 is narrower than the wider pin end 61, so that it is not possible to engage the surface 71 by the pin 57. This assures correct rotational alignment of plug 10 and receptacle 12 when they are to be mated.

Angularly displaced from the ramps 70 and 71 and-inwardly of the end of the receptacle shell 13 are flat surfaces 73 and 74. The planes of the surfaces 73 and 74 are parallel to the axis of the receptacle shell 13. At the forward ends of the flat surfaces 73 and 74 are transverse slots 75 and 76. The inner walls 77 and 78 of the slots 75 and 76 are radially inwardly of the flat surfaces 73 and 74, and also are parallel to the axis of the receptacle shell 13. The inner slot walls 77 and 78 extend at their ends to the cylindrical surface of the end portion 32 of the receptacle shell 13, so that the slots 75 and 76 are open sided.

A longitudinally aligned key 80 projects outwardly from the end portion 32 of the receptacle shell 13. The key 80 is adapted to mate with a complementary keyway 81 in the shell 20 of the plug 10. This provides a polarizing effect, assuring proper electrical interconnection between the contacts of the plug 10 and receptacle 12. The key 80, the end of which is inwardly of the outer edge of the end portion 32 of the receptacle shell 13, is misaligned with the keyway 81 when the pins 57 and 58 are opposite the ramp surfaces 70 and 71.

In connecting the plug 10 and receptacle 12, these two parts are positioned with the ends 61 and 62 of the pins 57 and 58 adjacent the ramp surfaces 70 and 71, respectively, as seen in FIG. 12. Indicator markings 82 and 83 on the end of the plug shell 20 and the end portion 32 of the receptacle shell 13 assist in so aligning the plug and receptacle. Then, the plug 10 and receptacle 12 are moved axially toward each other. This causes the ends 61 and 62 of the pins 57 and 58 to slide along the ramp surfaces 70 and 71, pushing the pins outwardly against the springs 65 and 66 to a retracted position. The pin ends 61 and 62 then bear against the cylindrical periphery of the end portion 32 of the receptacle shell 13, inwardly of the ramps 70 and 71. This relative axial movement of the plug 10 and receptacle 12 brings the end of the key 80 into engagement with a chamfered edge 84 formed on the inner corner of the end portion 43 of the plug shell )see FIG. 11). One end of the chamfered edge 84 is substantially aligned with the key 80 when the pins 57 and 58 are aligned with the ramp surfaces 70 and 71, respectively. From there, the chamfered edge extends to the keyway 81, as shown in FIG. 9. The engagement of the end of the key 80 with the edge 84 acts as a stop, limiting the amount of movement of the receptacle 12 toward the plug 10.

With the pins 57 and 58 in the retracted positions and bearing against the cylindrical wall of the end 32 of the receptacle shell 13 beyond the ramps 70 and 71, the receptacle 12 then is rotated relative to the plug 10. This rotation can be in only one direction, because the chamferededge 84 ends in an abutment 85 adjacent the initial position of the key 80 to prevent rotation in the opposite direction. Turning of the receptacle 12 relative to the plug 10 brings the key 80 into alignment with the keyway 81. This alignment of the key and keyway is accomplished automatically because the side edge 86 of the keyway 81 at the end of the chamfered edge 84 limits the amount of relative rotation. In this position of the plug 10 and receptacle 12, the ends 61 and 62 of the pins 57 and 58 engage the flat surfaces 73 and 74, respectively, of the receptacle shell 13, as seen in FIG. 13.

Additional relative axial movement between the plug 10 and receptacle 12 then is possible as the key 80 enters the keyway 81. This brings the plug 10 and receptacle 12 to the fully mated position in which the ends of the pins 16 are received in the socket contacts 29. In this position, the ends 61 and 62 of the pins 57 and 58 slide further back along the flat surfaces 73 and 74 on the end portion 32 of the receptacle shell 13. The outer ends of the pins 57'and 58 then project beyond the periphery of the enlarged annular portion 21 of the plug shell 20. This provides a visual indication'that the plug 10 and receptacle 12 are in the fully mated position.

With the plugs 10 and 11 and the receptacle 12 all in the completely mated condition, separation of the connector is effected by pulling outwardly in the axial direction on the plug 11. Typically, this will occur upon the firing of the rocket of a missile to which the plug 11 is attached. The circuit for the firing of the rocket is completed through the connector assembly. When the pull is exerted on the plug 11, a resistance to the separation of the plug 11 from the receptacle 12 is encountered by virtue of the coupling mechanism between these parts. The resilient force of the spring 48 tends to keep the balls 45 in the annular groove 52 of the receptacle shell 13 to maintain the connection at that point. However, there is no mechanism to preclude relative axial movement between the plug 10 and the receptacle 12, which are in a slidable relationship. Therefore, the force on the plugll will cause the receptacle 12 to be moved axially away from the plug 10. As this takes place, the ends 61 and 62 of the pins 57 and 58 slide outwardly along the flat surfaces 73 and 74 of the end portion 32 of the receptacle shell 13. Ultimately, the end portions 61 and 62 reach the transverse slots 75 and 76 whereupon the springs 65 and 66 force the pins inwardly to enter the slots. The pin ends then bear against the inner surfaces 77 and 78 of the transverse slots, as illustrated in FIGS. 4 and 14. This terminates the axial movement of the receptacle 12 relative to the plug 10, as the pin ends 61 and 62 act as stops cooperating with the abutments 87 and 88 provided by the outer sidewalls of the slots 75 and 76 to preclude further movement. Thus, limited axial movement of the receptacle 12 relative to the plug 10 is permitted until the pins enter the transverse slots 75 and 76.

This is a dead-face position in which the end of the plug 10 is covered by the receptacle 12. The parts are proportioned so that the pins 16 will have been separated from the socket contacts 29 by the time the movement of the receptacle is halted. Therefore, the electrical circuit through the connector is broken.

With the receptacle 12 then held against outward movement by the stationary plug 10, final separation of the connector occurs as the axial force continues to be applied to the plug 11. This force then overcomes :the resilient force of the breakaway coupling between the:plug 11 and the receptacle 12. The balls 45 are forced out of the groove 52 and the plug 11 is pulled free of the receptacle 12. The parts then are in the position shown in FIG. 5. No arcing can take place as the plug 11 leaves the receptacle 12 because the electrical circuit to the receptacle 12 was broken when the parts reached the dead-face position of FIG. 4. With the receptacle 12 positioned in front of the plug 10, the heat of the rocket blast will be deflected by the receptacle l-2-and prevented from damaging the plug 10. Therefore, while the receptacle 12 may be destroyed by the rocket heat, the plug 10 is protected from damage so that it may be reused later.

When the connector is in the 'dead-face position, it is not possible to reestablish the electrical connection by subsequent axial movement of the parts. The 'plug 10 and receptacle 12 cannot be moved back to the .mated position because of the stop resulting from the presence of the pin ends61 and 62 in the slots 75 and 76. The inner sidewalls 89 and of the slots 75 and 76 form abutments that cooperate with the pin ends 61 and 62, and prevent relative inwardzmovement of the plug and receptacle toward the mated position. This is an important feature in missile-launching systems, disarming the rocket-firing system once movement of the'missile has taken place.

Separation of the receptacle 12 from the plug 10 is effected quite easily and without the use of-any tooling. It is necessary merely to rotate the receptacle '12 relative to the plug 10 in either direction. When this occurs,'the ends 61 and 62 of the pins 57 and 58 are moved out of the slots 75 and 76 to bear against the cylindrical periphery of the end portion 32 of the receptacle shell 13. Then, the axial pull on the receptacle 12 separates it from the plug 10. The ability to accomplish the separation of the receptacle 12 fromthe plug 10 without tooling is a major advantage in a missile system, where adverse climatic or other conditions may make the use of special tooling for this purpose impossible. The receptacle 12 normally is furnished as a throwaway item to be replaced upon its destruction by the heat of the rocket blast. However, the plug 10, permanently installed in the missile launching'system, may be used indefinitely. The glass insert "15'of the receptacle will be damaged by the heat of the rocket,'-.but it will resist high temperatures adequately to shield andzprotect the plug 10 as the missile fires.

The flat surfaces 73 and 74 necessarily are located radially inwardly of the outer cylindrical periphery of the end portion 32 of the receptacle shell 13. As a result, the surfaces 73 and 74 are positioned radially inwardly of the outer edges of the forward walls 87 and 88 of the slots 75 and 76. Therefore, when the connector is mated and the pin ends 61 and 62 engage the surfaces 73 and 74, the inner edges of the pin ends are closer to the bottom walls 77 and 78 of the slots than are the outer edges of the forward walls-87 and 88. As a result, the walls 87 and-88 are in the paths ofthe pin ends 61 and'62 when the initial separation of the plug 10 and receptacle 12 takes place, and act as abutments engaged by the pins to assure entry of the pins into the slots 75 and 76. There is no danger that the pin ends 61 and 62will pass over the slots 75 and 76, and fail to hold the plug 10 and receptacle 12 in the dead-face position.

We claim:

1. An electrical connector device comprising a first, a second and a third unit,

electrical contact means in each or" said units,

said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit, thereby forming an electrical circuit from said second unit to said third unit through said first unit,

said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit,

said holding means being separable in response to a predetermined force urging said third unit relatively away from said first unit for allowing said third unit to move relatively away from said first unit, said second unit being movable relatively away from said first unit upon the exertion of a lesser force urging said second unit relatively away from said first unit, stop means for limiting the amount of movement of said second unit relatively away from said first unit to a second position in which said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween, and means for separating said first and second units when in said second position upon relative rotation of said first and second units. 2. An electrical connector device comprising a first, a second and a third unit, electrical contact means in each of said units,

said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit, thereby forming an electrical circuit from said second unit to said third unit through said first unit, said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit,

said holding means being separable in response to a predetermined force urging said third unit relatively away from said first unit for allowing said third unit to move relatively away from said first unit, said second unit being movable relatively away from said first unit upon the exertion of a lesser force urging said second unit relatively away from said first unit, and stop means for limiting the amount of movement of said second unit relatively away from said first unit to a second position in which said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween, said stop means including a spring-pressed means on one of said first and second units, and recess means in the other of said first and second units, said spring-pressed means being positioned to enter said recess means upon limited movement of said second unit relatively away from said first unit, said recess means including an open side portion for allowing disengagement of said spring-pressed means and said recess means upon relative rotation of said first and second units. 3. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position,

said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle,

said yieldable means being separable upon the exertion of a predetermined force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from said receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position,

said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position,

thereby breaking the electrical circuit from said second plug to said firstplug,

said stop means including at least one spring-pressed element carried by one of said receptacle and said second Plug,

and a duality of opposed walls defining a transverse slot in the other of said receptacle and second plug,

said spring-pressed element being positioned to enter said slot upon limited relative movement of said second plug separating said second plug from said opposite end of said receptacle,

whereupon said walls through said spring-element preclude further relative separating movement of said plug and said receptacle.

4. A device as recited in claim 3 in which said springpressed element is removable from said transverse slot upon relative rotation of said second plug and receptacle, for allowing complete separation of said second plug and receptacle upon said relative rotation.

5. A device as recited in claim 3 in which said electrical contact means of said receptacle includes at least one pin contact projecting toward either end of said receptacle, said electrical contact means of said first plug includes a first socket contact receiving one end portion of said pin contact, and said electrical contact means of said second plug includes a second socket contact receiving the opposite end portion of said pin contact.

6. A device as recited in claim 3 in which said receptacle includes a tubular shell, and a rigid insert in the central portion of said shell,

said electrical contact means of said receptacle includes at least one elongated pin the central portion of which is received in said rigid insert,

the end portions of said pin extending outwardly toward either end of said receptacle beyond said rigid insert,

said electrical contact means of said first plug includes a first socket contact receiving one end portion of said pin, and said electrical contact means of said second plug includes a second socket contact receiving the opposite end portion of said pin.

7. A device as recited in claim 6 in which said rigid insert is of glass material, whereby said rigid insert can withstand relatively high temperatures and insulate said second plug from a source of heat outwardly thereof.

8. A device as recited in claim 3 in which one of said transverse walls is relatively adjacent said springpressed element and the other of said transverse walls is relatively remote from said spring-pressed element, and including a surface aligned with said spring-pressed element and extending to said relatively adjacent transverse wall, said surface being inwardly of said slot relative to said remote transverse wall, whereby said spring-pressed element engages said surface upon said limited relative movement of said second plug, and said remote wall is in the path of said spring-pressed element for engagement thereby upon said limited relative movement of said second plug for assuring entry of said spring-pressed element 'into said slot. 9. An electrical connector device comprising a receptacle, a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle,

said yieldable means being separable upon the exertion of a predetermined'force relatively tending to move said first plug outwardly away from said one end of said receptacle, i said second plug including means for separating from receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, I said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said second plug including a tubular portion, said receptacle having a portion which is received in said tubular portion when said second plug and said receptacle are in said mated position, said stop means including at least one spring-pressed element extending through said tubular portion and bearing against the surface of said portion of said receptacle, said receptacle including a recess in said surface aligned with said spring-pressed element with respect to said tubular portion when said second plug and receptacle are in said mated position, whereupon upon said limited movement of said second plug relative to said receptacle said spring-pressed element enters said recess for precluding further relative axial movement of said second plug and said receptacle. 10. A device as recited in claim 9 in which said recess is defined by a transverse slot having an inner wall extending to an edge adjacent said surface, whereby said spring-pressed element is disengageable from said recess upon relative rotation of said second plug and receptacle,

11. A device as recited in claim 9'in' which said surface of said receptacle" includes an outer edge wall laterally displaced from said recess, said outer edge wall being inclined axially inwardly and radially outwardly for engaging said spring-pressed element and moving said spring-pressed element outwardly for engagement with said surface upon relative axial movement of said second plug toward said receptacle, said second plug and receptacle including second stop means engageable upon a predetermined limited amount of said relative axial movement of said second plug and receptacle, said second stop means being disengageable upon predetermined relative rotation of said second plug and receptacle to a position where said spring-pressed element is aligned with said recess, for thereby permitting additional relative axial movement of said second plug toward said receptacle to said mated position.

12. A device as recited in claim 11 in which said springpressed element includes a portion projecting outwardly beyond said tubular portion of said second plug when said spring-pressed element engages said surface of said receptacle, said portion of said spring-pressed element being retracted inwardly of said tubular portion upon movement of said spring-pressed element inwardly into said recess.

13. A device as recited in claim 11 in which there are two of said spring-pressed elements carried by said second plug, 7 each of said spring-pressed elements having an inner portion, said inner portionof one of said spring-pressed elements being wider than said inner portion of the other of said spring-pressed elements, said receptacle including two of said outer edge walls for engaging said inner portions of said spring-pressed elements, one of said outer edge walls being sufficiently wide to engage the narrower of said inner portions, but too narrow to engage the wider of said inner portions, for thereby allowing said predetermined limited relative axial movement only when said second plug and receptacle are in a predetermined rotational relationship. I

14. A device as recited in claim ll in which said second stop means includes a longitudinally extending key projecting outwardly from said surface of said receptacle, and a forward edge surface of said tubular portionof said second plug for engagement by said key,

said second plug having a keyway aligned with said key upon said predetermined relative rotation for effecting said disengagement of said second stop means.

15. A device as recited in claim 14 in which said forward edge surface of said tubular portion is recessed for said engagement by said key, said forward edge surface thereby providing an abutment at said keyway for limiting the amount of relative rotation of said second plug and receptacle to a position where said key is aligned with said keyway.

16. An electrical connector device comprising a receptacle,

a first plug engaging one end of said receptacle in a mated position,

a second plug engaging the opposite end of said receptacle in a mated position,

said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electricalcircuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle,

said yieldable means being separable upon the exertion of a predetermined force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separau'ng from said receptacleupon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said first plug including a tubular portion, said receptacle including a portion received in said tubular portion of said first plug when said first plug and receptacle are in said mated position, said yieldable coupling means for said first plug and receptacle including a plurality of balls, said tubular portion of said first plug having an aperture extending therethrough for each of said balls, said portion of said receptacle having a recess means therein, and spring means biasing said balls into said recess means for coupling said first plug and receptacle, said recess means having an inclined outer wall, whereby said balls are cammed out of said recess means and overcome the inward force of said spring means upon exertion of said predetermined force tending to move said first plug outwardly away from said one end ofsaid receptacle. 17. A device as recited in claim 16 in which said recess means is an annular groove in said portion of said receptacle.

18. A device as recited in claim l6' in which said spring means is a split annular member circumscribing said tubular portion of said firstplug.

19. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle,

said yieldable means being separable upon the exertion of a predetermined force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from said receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end,

and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said stop means including at least one spring-pressed element carried by one of said receptacle and second plug, the other of said receptacle and second plug having a recess aligned with said spring-pressed element and dimensioned to receive the same upon said separation of said second plug from said receptacle, and having a surface aligned with said spring-pressed element and engageable thereby upon said separation of said second plug from said receptacle, said recess having an abutment on the side thereof remote from said spring-pressed element, said surface extending to said recess and being inwardly of said recess relative to said abutment,

whereby said abutment is in the path of said springpressed element for engagement thereby upon said separation of said second plug from said receptacle for assuring entry of said spring-pressed element into said recess. 20. An electrical connector device comprising a first, a second and a third unit, electrical contact means in each of said units,

said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit, thereby forming an electrical circuit from said second unit to said third unit through said first unit, said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof'upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit,

said holding means being separable in response to a predetermined axial force urging said third unit relatively away from said first unit for allowing said third unit to move axially relatively away from said first unit, said second unit being movable axially relatively away from said first unit upon the exertion of a lesser axial force urging said second unit relatively away from said first unit, stop means for limiting the amount of such movement of said second unit relatively away from said first unit to a second position in which said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween, and means for preventing relative movement of said first and second units from said second position to said mated position in response to an axial force urging said third unit toward said second unit. 21. An electrical connector device comprising a first, a second and a third unit, electrical contact means in each of said units,

said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit,

thereby forming an electrical circuit from said second unit to said third unit through said first unit, said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit,

said holding means being separable in response to a predetermined axial force urging said third unit relatively away from said first unit for allowing said third unit to move axially relatively away from said first unit, said second unit being movable axially relatively away from said first unit upon the exertion of a lesser axial force urging said second unit relatively away from said first unit, and stop means for limiting the amount of such movement of said second unit relatively away from said first unit to a second position in which said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween said stop means including a spring-pressed means on one of said first and second units, and recess means in the other of said first and second units, said spring-pressed means being positioned to enter said recess means upon limited axial movement of said second unit relatively away' from said first unit, said recess means presenting an abutment means for engagement by said spring-pressed means for preventing relative movement of said first and second units from said second position to said mated position in response to an axial force urging said third unit toward said second unit. 22. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle,

said yieldable means being separable upon the exertion of a predetermined axial force relatively tending'to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from said receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug axially outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled axially relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative axial movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug,

said stop means including means for normally precluding relative axial movement of said second plug and said receptacle to said mated position subsequent to said movement of said second plug and said receptacle to said second position upon the exertion of an axial force urging said first plug and receptacle toward said second plug. 

1. An electrical connector device comprising a first, a second and a third unit, electrical contact means in each of said units, said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit, thereby forming an electrical circuit from said second unit to said third unit through said first unit, said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit, said holding means being separable in response to a predetermined force urging said third unit relatively away from said first unit for allowing said third unit to move relatively away from said first unit, said second unit being movable relatively away from said first unit upon the exertion of a lesser force urging said second unit relatively away from said first unit, stop means for limiting the amount of movement of said second unit relatively away from said first unit to a second position in whicH said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween, and means for separating said first and second units when in said second position upon relative rotation of said first and second units.
 2. An electrical connector device comprising a first, a second and a third unit, electrical contact means in each of said units, said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit, thereby forming an electrical circuit from said second unit to said third unit through said first unit, said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit, said holding means being separable in response to a predetermined force urging said third unit relatively away from said first unit for allowing said third unit to move relatively away from said first unit, said second unit being movable relatively away from said first unit upon the exertion of a lesser force urging said second unit relatively away from said first unit, and stop means for limiting the amount of movement of said second unit relatively away from said first unit to a second position in which said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween, said stop means including a spring-pressed means on one of said first and second units, and recess means in the other of said first and second units, said spring-pressed means being positioned to enter said recess means upon limited movement of said second unit relatively away from said first unit, said recess means including an open side portion for allowing disengagement of said spring-pressed means and said recess means upon relative rotation of said first and second units.
 3. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle, said yieldable means being separable upon the exertion of a predetermined force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from said receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug AND said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said stop means including at least one spring-pressed element carried by one of said receptacle and said second plug, and a duality of opposed walls defining a transverse slot in the other of said receptacle and second plug, said spring-pressed element being positioned to enter said slot upon limited relative movement of said second plug separating said second plug from said opposite end of said receptacle, whereupon said walls through said spring-element preclude further relative separating movement of said plug and said receptacle.
 4. A device as recited in claim 3 in which said spring-pressed element is removable from said transverse slot upon relative rotation of said second plug and receptacle, for allowing complete separation of said second plug and receptacle upon said relative rotation.
 5. A device as recited in claim 3 in which said electrical contact means of said receptacle includes at least one pin contact projecting toward either end of said receptacle, said electrical contact means of said first plug includes a first socket contact receiving one end portion of said pin contact, and said electrical contact means of said second plug includes a second socket contact receiving the opposite end portion of said pin contact.
 6. A device as recited in claim 3 in which said receptacle includes a tubular shell, and a rigid insert in the central portion of said shell, said electrical contact means of said receptacle includes at least one elongated pin the central portion of which is received in said rigid insert, the end portions of said pin extending outwardly toward either end of said receptacle beyond said rigid insert, said electrical contact means of said first plug includes a first socket contact receiving one end portion of said pin, and said electrical contact means of said second plug includes a second socket contact receiving the opposite end portion of said pin.
 7. A device as recited in claim 6 in which said rigid insert is of glass material, whereby said rigid insert can withstand relatively high temperatures and insulate said second plug from a source of heat outwardly thereof.
 8. A device as recited in claim 3 in which one of said transverse walls is relatively adjacent said spring-pressed element and the other of said transverse walls is relatively remote from said spring-pressed element, and including a surface aligned with said spring-pressed element and extending to said relatively adjacent transverse wall, said surface being inwardly of said slot relative to said remote transverse wall, whereby said spring-pressed element engages said surface upon said limited relative movement of said second plug, and said remote wall is in the path of said spring-pressed element for engagement thereby upon said limited relative movement of said second plug for assuring entry of said spring-pressed element into said slot.
 9. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle, said yieldable means being separable upon the exertion of a predetermined force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said second plug including a tubular portion, said receptacle having a portion which is received in said tubular portion when said second plug and said receptacle are in said mated position, said stop means including at least one spring-pressed element extending through said tubular portion and bearing against the surface of said portion of said receptacle, said receptacle including a recess in said surface aligned with said spring-pressed element with respect to said tubular portion when said second plug and receptacle are in said mated position, whereupon upon said limited movement of said second plug relative to said receptacle said spring-pressed element enters said recess for precluding further relative axial movement of said second plug and said receptacle.
 10. A device as recited in claim 9 in which said recess is defined by a transverse slot having an inner wall extending to an edge adjacent said surface, whereby said spring-pressed element is disengageable from said recess upon relative rotation of said second plug and receptacle.
 11. A device as recited in claim 9 in which said surface of said receptacle includes an outer edge wall laterally displaced from said recess, said outer edge wall being inclined axially inwardly and radially outwardly for engaging said spring-pressed element and moving said spring-pressed element outwardly for engagement with said surface upon relative axial movement of said second plug toward said receptacle, said second plug and receptacle including second stop means engageable upon a predetermined limited amount of said relative axial movement of said second plug and receptacle, said second stop means being disengageable upon predetermined relative rotation of said second plug and receptacle to a position where said spring-pressed element is aligned with said recess, for thereby permitting additional relative axial movement of said second plug toward said receptacle to said mated position.
 12. A device as recited in claim 11 in which said spring-pressed element includes a portion projecting outwardly beyond said tubular portion of said second plug when said spring-pressed element engages said surface of said receptacle, said portion of said spring-pressed element being retracted inwardly of said tubular portion upon movement of said spring-pressed element inwardly into said recess.
 13. A device as recited in claim 11 in which there are two of said spring-pressed elements carried by said second plug, each of said spring-pressed elements having an inner portion, said inner portion of one of said spring-pressed elements being wider than said inner portion of the other of said spring-pressed elements, said receptacle including two of said outer edge walls for engaging said inner portions of said spring-pressed elements, one of said outer edge walls being sufficiently wide to engage the narrower of said inner portions, but too narrow to engage the wider of said Inner portions, for thereby allowing said predetermined limited relative axial movement only when said second plug and receptacle are in a predetermined rotational relationship.
 14. A device as recited in claim 11 in which said second stop means includes a longitudinally extending key projecting outwardly from said surface of said receptacle, and a forward edge surface of said tubular portion of said second plug for engagement by said key, said second plug having a keyway aligned with said key upon said predetermined relative rotation for effecting said disengagement of said second stop means.
 15. A device as recited in claim 14 in which said forward edge surface of said tubular portion is recessed for said engagement by said key, said forward edge surface thereby providing an abutment at said keyway for limiting the amount of relative rotation of said second plug and receptacle to a position where said key is aligned with said keyway.
 16. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle, said yieldable means being separable upon the exertion of a predetermined force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from said receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said first plug including a tubular portion, said receptacle including a portion received in said tubular portion of said first plug when said first plug and receptacle are in said mated position, said yieldable coupling means for said first plug and receptacle including a plurality of balls, said tubular portion of said first plug having an aperture extending therethrough for each of said balls, said portion of said receptacle having a recess means therein, and spring means biasing said balls into said recess means for coupling said first plug and receptacle, said recess means having an inclined outer wall, whereby said balls are cammed out of said recess means and overcome the inward force of said spring means upon exertion of said predetermined force tending to move said first plug outwardly away from said one end of said receptacle.
 17. A device as recited in claim 16 in which said recess means is an annular groove in said portion of said receptacle.
 18. A device as recited in claim 16 in which said spring means is a split annular member circumscribing said tubular portion of said first plug.
 19. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a matEd position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle, said yieldable means being separable upon the exertion of a predetermined force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from said receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said stop means including at least one spring-pressed element carried by one of said receptacle and second plug, the other of said receptacle and second plug having a recess aligned with said spring-pressed element and dimensioned to receive the same upon said separation of said second plug from said receptacle, and having a surface aligned with said spring-pressed element and engageable thereby upon said separation of said second plug from said receptacle, said recess having an abutment on the side thereof remote from said spring-pressed element, said surface extending to said recess and being inwardly of said recess relative to said abutment, whereby said abutment is in the path of said spring-pressed element for engagement thereby upon said separation of said second plug from said receptacle for assuring entry of said spring-pressed element into said recess.
 20. An electrical connector device comprising a first, a second and a third unit, electrical contact means in each of said units, said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit, thereby forming an electrical circuit from said second unit to said third unit through said first unit, said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit, said holding means being separable in response to a predetermined axial force urging said third unit relatively away from said first unit for allowing said third unit to move axially relatively away from said first unit, said second unit being movable axially relatively away from said first unit upon the exertion of a lesser axial force urging said second unit relatively away from said first unit, stop means for limiting the amount of such movement oF said second unit relatively away from said first unit to a second position in which said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween, and means for preventing relative movement of said first and second units from said second position to said mated position in response to an axial force urging said third unit toward said second unit.
 21. An electrical connector device comprising a first, a second and a third unit, electrical contact means in each of said units, said first, second and third units being in adjacency in a mated position in which said electrical contact means of said first unit are engaged with said electrical contact means of said second unit and said electrical contact means of said first unit are engaged with said electrical contact means of said third unit, thereby forming an electrical circuit from said second unit to said third unit through said first unit, said electrical contact means of said first and second units including means for effecting disengagement thereof upon relative movement of said second unit away from said first unit, said electrical contact means of said first and third units including means for effecting disengagement thereof upon relative movement of said first unit away from said third unit, means yieldably holding said third unit to said first unit, said holding means being separable in response to a predetermined axial force urging said third unit relatively away from said first unit for allowing said third unit to move axially relatively away from said first unit, said second unit being movable axially relatively away from said first unit upon the exertion of a lesser axial force urging said second unit relatively away from said first unit, and stop means for limiting the amount of such movement of said second unit relatively away from said first unit to a second position in which said electrical contact means of said second unit and said electrical contact means of said first unit are disengaged, thereby breaking the electrical circuit therebetween said stop means including a spring-pressed means on one of said first and second units, and recess means in the other of said first and second units, said spring-pressed means being positioned to enter said recess means upon limited axial movement of said second unit relatively away from said first unit, said recess means presenting an abutment means for engagement by said spring-pressed means for preventing relative movement of said first and second units from said second position to said mated position in response to an axial force urging said third unit toward said second unit.
 22. An electrical connector device comprising a receptacle, a first plug engaging one end of said receptacle in a mated position, a second plug engaging the opposite end of said receptacle in a mated position, said receptacle, said first plug and said second plug each having electrical contact means therein, said electrical contact means of said first and second plugs being in engagement with said electrical contact means of said receptacle, whereby an electrical circuit is formed between said first and second plugs through said receptacle, yieldable means coupling said first plug to said receptacle, said yieldable means being separable upon the exertion of a predetermined axial force relatively tending to move said first plug outwardly away from said one end of said receptacle, said second plug including means for separating from said receptacle upon the exertion of a force less than said predetermined force relatively tending to move said second plug axially outwardly away from said opposite end of said receptacle, whereby when said first and second plugs are pulled axially relatively away from said ends of said receptacle said second plug initially separates from said receptacle at said opposite end and said first plug subsequently separates from said receptacle at said one end, and stop means for limiting the amount of relative axial movement separating said second plug from said opposite end of said receptacle and for holding said second plug and said receptacle in a second relative position, said contact means of said receptacle and of said second plug being disengaged when said second plug and said receptacle are in said second position, thereby breaking the electrical circuit from said second plug to said first plug, said stop means including means for normally precluding relative axial movement of said second plug and said receptacle to said mated position subsequent to said movement of said second plug and said receptacle to said second position upon the exertion of an axial force urging said first plug and receptacle toward said second plug. 